Automotive PV module charges drive, 12V batteries

The Hit modules generate ample power even if the temperature is high in an installation environment or when the installation area is limited.

Panasonic's recently developed Hit photovoltaic module for automobiles has been tapped to power Toyota Motor's new Prius PHV.

The Hit PV modules have been well received in the residential solar power generation system market, according to Panasonic. The modules' biggest features include the ability to generate ample power effectively even if the temperature is high in an installation environment or when the installation area is limited. These features are optimal for automotive photovoltaic modules, and were created by heterojunction solar cells, which Panasonic developed independently.

The surface of a silicon substrate is covered by an amorphous silicon film, which allows the retrieval of electrically charged particles that are generated within solar cells without omission and eventually achieves high output, according to the company.

The rated output is the value of the power output when the module temperature is 25°C. In principle, the output of solar cells decreases when the temperature rises. On a summer day, the exterior temperature including the vehicle's roof can reach 80°C or higher. When photovoltaic modules are mounted on a vehicle, output decreases as much or more than it does when they are mounted on residential roofs. However, any output decline is minimised because the temperature coefficient of output of Panasonic’s heterojunction solar cells is smaller compared to general solar cells.

These solar cells are equipped with two optimal features as automotive solar cells, namely high output and resistance to a hot environment (less output decline).

Although photovoltaic modules were installed as an option in the previous Prius HV, their applications were limited to areas such as ventilation for in-vehicle air-conditioning. Conventional automotive solar cells can output up to several tens of watts and have been used only for the auxiliary charging of 12V batteries and ventilation power sources for parked cars. Panasonic's solar cells, in comparison, allow a high output of about 180W—three times more than the conventional output—in a limited area on a car's roof, enabling the charging of the drive lithium-ion batteries as well as 12V batteries.

Electrical energy generated from solar cells can be applied to the charging of driving power sources, extending travel distance per charge, according to the company.

Panasonic has also developed a unique lamination technology that conforms to the new Prius PHV's three-dimensional curved roof. This technology features the thermal compression bonding of the upper and lower module surfaces with flexible material and also allows the manufacturing process to address three-dimensional curves in addition to conventional flat surfaces.

And as with the Prius PHV that was released in 2012, Panasonic's automotive prismatic lithium-ion batteries have also been adopted for the drive batteries of the new Prius PHV. These batteries balance the required for automotive batteries, including high capacity, high output and high safety levels, as well as charge regenerated energy and electrical energy that has been generated by solar cells to extend an EV's travel distance and increased fuel economy.